According to my knowledge Discovery is for server not for client.
Client information is shown from the registry key hkey_local_machine\software\intel\landesk\virusprotect6\currentversion\Clients
When a client connects to SAV server it creates a new entry in the above mentioned key.
You can reduce the time out value so that clients will be deleted.
If the client doesnt exists it will be deleted from console...
Reg Path
HKEY_LOCAL_MACHINE\SOFTWARE\Intel\LANDesk\VirusProtect6\CurrentVersion
Value Name (Decimal)
ClientExpirationTimeout
Default Value is 720
(720 Hrs - 30 Days)
REF:
http://service1.symantec.com/support/ent-security.nsf/docid/2000070511575548
How many servers you have in your setup.
If the client is in some other server then you may have to delete it from other server's registry...